ForEach-Object for iteration in PowerShell - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print each number in the list using ForEach-Object.

PowerShell

1, 2, 3, 4, 5 | ForEach-Object [1] { Write-Output $_ }

Drag options to blanks, or click blank then click option'

A-ScriptBlock

B-Process

C-FilterScript

D-InputObject

Attempts:

3 left

💡 Hint

Common Mistakes

Using -InputObject instead of -Process causes errors.

Trying to use -FilterScript which is not a valid parameter.

The -Process parameter is used with ForEach-Object to specify the script block to run for each item.

2fill in blank

medium

Complete the code to multiply each number by 2 and output the result.

PowerShell

1, 2, 3 | ForEach-Object -Process { $_ [1] 2 }

Drag options to blanks, or click blank then click option'

A+

B/

C-

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using + adds 2 instead of multiplying.

Using / divides the number.

The * operator multiplies each number by 2.

3fill in blank

hard

Fix the error in the code to correctly output each item in uppercase.

PowerShell

'apple', 'banana', 'cherry' | ForEach-Object -Process { $_.[1]() }

Drag options to blanks, or click blank then click option'

AUpperCase

Btoupper

CToUpper

DtoUpperCase

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase method names causes errors.

Using JavaScript style method names like toUpperCase.

The correct method name in PowerShell to convert a string to uppercase is ToUpper().

4fill in blank

hard

Fill both blanks to filter numbers greater than 3 and square them.

PowerShell

1, 2, 3, 4, 5 | Where-Object { $_ [1] 3 } | ForEach-Object -Process { $_ [2] $_ }

Drag options to blanks, or click blank then click option'

A>

B<

C*

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using < filters numbers less than 3, which is wrong here.

Using + adds numbers instead of squaring.

Use > to filter numbers greater than 3, and * to square each number.

5fill in blank

hard

Fill all three blanks to create a hashtable $h of words and their lengths for words longer than 4 letters.

PowerShell

$h = @{}; 'apple', 'bat', 'carrot', 'dog' | ForEach-Object { if ( $_.Length [1] 4 ) { $h[[2]] = $_.[3] } }

Drag options to blanks, or click blank then click option'

A-gt

B$_

CLength

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using -lt filters short words instead.

Using a literal instead of $_ for the key.

Using lowercase 'length' which does not match the Length property.

Use -gt to check greater than 4, $_ as the key (the word), and Length as the property for the value (length).

Practice

1. What does the ForEach-Object cmdlet do in PowerShell?

easy

A. Runs a block of code on each item in a collection

B. Creates a new object from a template

C. Deletes items from a list

D. Sorts items in a collection

Solution

1. Step 1: Understand the purpose of ForEach-Object

   ForEach-Object is designed to process each item in a collection by running a script block on it.

2. Step 2: Compare with other options

   Options A, B, and C describe different cmdlets or actions unrelated to iteration over items.

3. Final Answer:

   Runs a block of code on each item in a collection -> Option A

4. Quick Check:

   ForEach-Object = runs code on each item [OK]

Hint: Remember: ForEach-Object processes items one by one [OK]

Common Mistakes:

• Confusing ForEach-Object with sorting or filtering cmdlets
• Thinking it creates or deletes objects
• Assuming it works only on arrays, not collections

2. Which of the following is the correct syntax to use ForEach-Object to print each item in a list?

easy

A. 1..3 | ForEach-Object { Write-Output $_ }

B. ForEach-Object 1..3 { Write-Output $_ }

C. Write-Output 1..3 | ForEach-Object $_

D. 1..3 ForEach-Object { $_ }

Solution

1. Step 1: Identify correct pipeline usage

   In PowerShell, ForEach-Object is used after a pipeline to process each item, so the syntax is: collection | ForEach-Object { script }

2. Step 2: Check the script block and variable usage

   The script block uses $_ to refer to the current item. 1..3 | ForEach-Object { Write-Output $_ } correctly uses this syntax.

3. Final Answer:

   1..3 | ForEach-Object { Write-Output $_ } -> Option A

4. Quick Check:

   Pipeline + ForEach-Object + { $_ } = correct syntax [OK]

Hint: Use pipeline before ForEach-Object and $_ inside braces [OK]

Common Mistakes:

• Placing ForEach-Object before the collection
• Not using curly braces for the script block
• Using $_ outside the script block

3. What is the output of this PowerShell command?

1..3 | ForEach-Object { $_ * 2 }

medium

A. 3 6 9

B. 1 2 3

C. 2 4 6

D. Error: Cannot multiply

Solution

1. Step 1: Understand the input and operation

   The input is numbers 1, 2, 3. ForEach-Object multiplies each by 2.

2. Step 2: Calculate each iteration

   1*2=2, 2*2=4, 3*2=6, so output is 2 4 6.

3. Final Answer:

   2 4 6 -> Option C

4. Quick Check:

   Each item * 2 = 2 4 6 [OK]

Hint: Multiply each item inside ForEach-Object with $_ [OK]

Common Mistakes:

• Assuming output is original numbers
• Confusing multiplication with addition
• Expecting an error due to syntax

4. Identify the error in this script:

1..3 | ForEach-Object { Write-Output $item }

medium

A. ForEach-Object cannot process number ranges

B. Missing pipeline operator before ForEach-Object

C. Incorrect use of Write-Output cmdlet

D. Variable $item is undefined inside the script block

Solution

1. Step 1: Check variable usage inside ForEach-Object

   Inside ForEach-Object, the current item is referenced by $_, not $item.

2. Step 2: Verify other syntax elements

   The pipeline and Write-Output usage are correct, and ForEach-Object can process number ranges.

3. Final Answer:

   Variable $item is undefined inside the script block -> Option D

4. Quick Check:

   Use $_ for current item, not $item [OK]

Hint: Use $_ inside ForEach-Object, not custom variable names [OK]

Common Mistakes:

• Using undefined variables instead of $_
• Forgetting the pipeline operator
• Misunderstanding ForEach-Object capabilities

5. You have a list of file names: @('file1.txt', 'file2.txt.log', 'file3.txt'). Using ForEach-Object, how do you print only the names ending with '.txt'?

hard

A. @('file1.txt', 'file2.txt.log', 'file3.txt') | ForEach-Object { $_.EndsWith('.txt') }

B. @('file1.txt', 'file2.txt.log', 'file3.txt') | ForEach-Object { if ($_ -like '*.txt') { Write-Output $_ } }

C. @('file1.txt', 'file2.txt.log', 'file3.txt') | ForEach-Object { Write-Output $_ -like '*.txt' }

D. @('file1.txt', 'file2.txt.log', 'file3.txt') | ForEach-Object { if ($_.Contains('.txt')) { $_ } }

Solution

1. Step 1: Understand filtering inside ForEach-Object

   To print only items ending with '.txt', use an if condition with -like '*.txt' inside the script block.

2. Step 2: Check each option's correctness

   @('file1.txt', 'file2.txt.log', 'file3.txt') | ForEach-Object { if ($_ -like '*.txt') { Write-Output $_ } } correctly uses if with -like and Write-Output. @('file1.txt', 'file2.txt.log', 'file3.txt') | ForEach-Object { Write-Output $_ -like '*.txt' } uses invalid syntax (Write-Output does not accept -like as parameter). @('file1.txt', 'file2.txt.log', 'file3.txt') | ForEach-Object { $_.EndsWith('.txt') } outputs boolean values instead of filtered names. @('file1.txt', 'file2.txt.log', 'file3.txt') | ForEach-Object { if ($_.Contains('.txt')) { $_ } } uses Contains which matches anywhere, not just the end (prints all three).

3. Final Answer:

   @('file1.txt', 'file2.txt.log', 'file3.txt') | ForEach-Object { if ($_ -like '*.txt') { Write-Output $_ } } -> Option B

4. Quick Check:

   Use if + -like '*.txt' inside ForEach-Object [OK]

Hint: Use if ($_ -like '*.txt') inside ForEach-Object to filter [OK]

Common Mistakes:

• Outputting boolean results instead of filtered items
• Using string methods incorrectly in PowerShell
• Using Contains instead of EndsWith or -like for suffix